Sensory system must both detect and discriminate stimuli in the environment. The elucidation of the neural basis of these processes is arduous, but an important goal in neuroscience. Our current understanding of the mammalian gustatory stem remains at a rather rudimentary level. This derives, to a large extent, from the failure to coordinate behavioral and neurophysiological approaches to the problem of taste coding in both the peripheral and central nervous system. The overall goal of the proposed project is to specify formal correspondences between the measured psychophysical characteristic of the animal and the electrophysiological properties characterizing peripheral taste afferents. Such an endeavor will generate data that will provide critical insight into the neural coding process. The experiments proposed here are designed to make refined psychophysical assessments of taste function before and after selective gustatory nerve transection n rats. The behavioral tasks are designed to measure the detectability, the suprathreshold taste functions, and the between-stimulus discriminability associated with an array of taste compounds chosen on the basis of their current theoretical relevance. The taste nerves to be examined and their respective oropharyngeal receptive fields are:1) the chorda tympani nerve which innervates the anterior tongue, 2) the glossopharyngeal nerve which innervates the palate. These 3 nerves collectively account for 90- 96% of the total taste bud population. The behavioural results generated by this research will be compared with the electrophysiological findings in the literature. Thus, the taste stimuli and concentrations chosen are consistent with published electrophysiological data. The specific aims of this research are: 1) to specify the relative contribution of the various gustatory nerves to taste sensibility in an effort to reveal the peripheral organization of the gustatory system; 2) to identify significant features of the neural coding process by comparing psychophysically measured changes in sensory function as a result of specific nerve transection with the known response properties of afferents form both the removed and remaining fields; and 3) to provide a consistent parametric psychophysical data base for rat gustation to guide the analysis and interpretation of neurophysiological findings in both the peripheral and central nervous system. A better understanding of the neural organization of taste processes should facilitate the diagnosis and treatment of chemosensory and neurological disorders.